Adaptive feedback control system and method for voltage regulators

ABSTRACT

A voltage regulator includes a first feedback circuit, a second feedback circuit, and a feedback signal adaptive circuit. The first voltage feedback circuit includes an amplifier that is configured to generate a compensation signal according to a feedback signal from an output of the voltage regulator and a reference voltage, while the second voltage feedback circuit includes a comparator that is configured to generate a PWM signal to drive a switch circuit in which the comparator initiates the PWM pulse when the feedback voltage goes lower than the compensation signal and ends the PWM pulse when the sum of the feedback signal and a ramp signal exceeds the sum of the compensation signal and a threshold signal. The feedback signal adaptive circuit modifies the feedback signal according to changes in an input voltage of the voltage regulator and a control signal.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to U.S. Provisional Application No.62/277112, filed on Jan. 11, 2016, entitled “ADAPTIVE FEEDBACK CONTROLSYSTEM AND METHOD FOR VOLTAGE REGULATORS,” invented by Gang CHEN, and isincorporated herein by reference and priority thereto for common subjectmatter is hereby claimed.

TECHNICAL FIELD

Aspects of the present disclosure relate to voltage regulators and, inparticular, to an adaptive feedback control system and method forvoltage regulators.

BACKGROUND

Voltage regulators are commonly used for providing electrical power witha stable voltage. A particular type of voltage regulator includes aswitching regulator that controls an output voltage of the voltageregulator using one or more switches that are switched on and off with aduty cycle proportional to a measured output voltage of an output of thevoltage regulator. The switches typically include metal-oxidesemiconductor field effect transistor (MOSFETs) devices that arecontrolled by a switching circuit, such as a pulse-width-modulation(PWM) circuit in which the pulse width is modulated according to changesin output voltage, or a constant on time (COT) circuit in which pulsewidth is maintained constant while a duration between pulses ismodulated according to changes in output voltage.

SUMMARY

According to one aspect, a voltage regulator includes a first feedbackcircuit, a second feedback circuit, and a feedback signal adaptivecircuit. The first voltage feedback circuit includes an amplifier thatis configured to generate a compensation signal according to a feedbacksignal from an output of the voltage regulator and a reference voltage,while the second voltage feedback circuit includes a comparator that isconfigured to generate a PWM signal to drive a switch circuit in whichthe comparator initiates the PWM pulse when the feedback voltage goeslower than the compensation signal and ends the PWM pulse when the sumof the feedback signal and a ramp signal exceeds the sum of thecompensation signal and a threshold signal. The feedback signal adaptivecircuit modifies the feedback signal according to changes in an inputvoltage of the voltage regulator and a control signal.

BRIEF DESCRIPTION OF THE DRAWINGS

The various features and advantages of the technology of the presentdisclosure will be apparent from the following description of particularembodiments of those technologies, as illustrated in the accompanyingdrawings. It should be noted that the drawings are not necessarily toscale; however the emphasis instead is being placed on illustrating theprinciples of the technological concepts. Also, in the drawings the likereference characters may refer to the same parts throughout thedifferent views. The drawings depict only typical embodiments of thepresent disclosure and, therefore, are not to be considered limiting inscope.

FIG. 1 illustrates an example switching voltage regulator that may beprovided with adaptive feedback control according to one embodiment ofthe present disclosure.

FIG. 2 illustrates another example switching voltage regulator that maybe provided with adaptive feedback control according to one embodimentof the present disclosure.

FIG. 3 illustrates yet another example switching voltage regulator thatmay be provided with adaptive feedback control according to oneembodiment of the present disclosure.

DETAILED DESCRIPTION

Aspects of a control circuit topology described herein provide a circuitand method for voltage regulation using a first feedback circuit thatprovides for precise static control of the output voltage, a secondfeedback circuit that provides for dynamic control of the outputvoltage, and a feedback signal adaptive circuit that adapts how thesecond feedback circuit dynamically controls the voltage regulatoraccording to changes in the input voltage and/or a control input. Thecontrol input may be coupled to any suitable source, such as the outputof the voltage regulator for providing enhanced control over transientchanges in loading, to an external signal for providing feed-forwardcontrol, or to the output of a switch circuit for implementations wheredirect sensing of the output voltage may not be readily available.

Switching voltage regulators are a particular type of voltage regulatorthat controls an output voltage using a switching circuit that isswitched on and off with a duty cycle proportional to a measured outputvoltage of the voltage regulator. These switching voltage regulators mayinclude circuitry to generate a PWM signal having fixed switchingfrequency, or they may include circuitry that generates the PWM signalvia astable multivibrator operation (e.g., the PWM signal turns on oroff according to one or more quiescent sense points in the voltageregulator). Those switching voltage regulators that function accordingto an astable multivibrator topology may be more cost effective thanother types of voltage regulator topologies because, among other things,they can often be implemented with fewer parts.

Use of switching voltage regulators may provide enhanced efficiency overconventional regulators by reducing or limiting a voltage drop acrosscertain control elements in the voltage regulator. That is, a switchingvoltage regulator regulates its output by alternatively switching one ormore switches on (e.g., logic hi) and off (e.g., logic lo) with a dutycycle sufficient to maintain regulation while keeping the switches at ornear a saturated condition in either their on or off states.Nevertheless, the use of switching voltage regulators has severalchallenges to be overcome to ensure their proper operation. For example,because it would be beneficial to provide a switching voltage regulatorhaving a minimum number of components, many currently availableswitching voltage regulators are often provided by integrated circuit(IC) chips in which one or more of the components of the switchingvoltage regulators are integrated into a single package. Nevertheless,external compensation networks having numerous external components areoften required to ensure that the switching voltage regulator remainsstable over large changes in operating conditions (e.g., transientloading conditions, changes in input voltage, etc.). Additionally,maintaining adequate efficiency over a wide range of output conditions(e.g., no load to full load) is often difficult to obtain. In manycases, switching voltage regulators are designed against many operatingfactors, such as current consumption, transient performance, bandwidthlimitations, component quantity, and overall component costs, which canoften require the addition of more components.

One particular type of topology that has been introduced to solve someof these problems includes a V² control circuit topology. The V² controlcircuit topology generally includes two feedback paths in which a firstfeedback path includes an error amplifier to provide precise outputcontrol, and a second feedback path to correct for transient changes inthe output voltage of the switching voltage regulator. However, V²control circuit topologies are not readily adaptable to loads withcapacitors having low equivalent series resistance (ESR) (e.g., ceramiccapacitors, tantalum capacitors, etc.). The stability of V² controlcircuits are also sensitive to filter variations and printed circuitboard (PCB) layout.

FIG. 1 illustrates an example switching voltage regulator 100 that maybe provided with adaptive feedback control according to one embodimentof the present disclosure. The switching voltage regulator 100, in thisparticular case is a synchronous buck converter that converts an inputvoltage (Vin) to an output voltage (Vout). In other embodiments, anysuitable type of switching voltage regulator may be provided withadaptive feedback control, such as boost converters, buck-boostconverters, or other type of switching voltage regulators. The switchingvoltage regulator 100 includes a gate drive circuit 102, a switchingcircuit 104, an inductor 106, a first feedback circuit 108, a secondfeedback circuit 110, a feedback signal adaptive circuit 112, and a rampgeneration circuit 114. Although one particular type of switchingvoltage regulator 100 is shown, it should be understood that otherembodiments may include additional, fewer, or different componentsand/or circuitry than what is shown and described herein withoutdeparting from the spirit and scope of the present disclosure.

The second feedback circuit 110 generates a PWM signal that is fed tothe switching circuit 104, via the drive circuit 102, to selectivelyapply electrical power from the input (Vin) to the output (Vout), whichmay be coupled to a load 118 and a capacitor 120. The second feedbackcircuit 110 generally includes a multi-input comparator 122 and aminimum off time circuit 124. The comparator 122 is responsive to athreshold voltage (Vth), a ramp signal provided by the ramp circuit 114,a feedback (FB) signal, and a compensation (COMP) signal provided by thefirst feedback circuit 108 to alternatively change from an on state(e.g., logic hi) to an off state (e.g., logic lo) for switching theswitch circuit 104 via the gate drive circuit 102. Moreover, apulse-width modulated (PWM) pulse is initiated when the feedback voltagegoes lower than the COMP signal and ended when the sum of the feedbackFB signal and the RAMP signal exceeds the sum of the compensation signaland the threshold signal.

The minimum off time circuit 124 is provided to ensure that the PWMsignal continues to switch between on and off states, such as whenrelatively large loading conditions are incurred on the output voltage(Vout). That is, the minimum off time circuit 124 assures the off timeoccurs in the PWM signal after each on time is longer in duration than aminimum value. Such behavior may be good for operation of gate driversand current sense circuits based on low-side switches that cannotinherently sense overloading conditions during the on time of the PWMsignal. Nevertheless, the minimum off time circuit 124 may be omitted ifnot needed for proper operation of the switching voltage regulator 100.The minimum off time circuit 124 includes a monostable generator thatgenerates a pulse with a specified duration (e.g., 100 nano-seconds).The pulse is used to gate the PWM signal from the second feedbackcircuit 110 such that, in the event that the comparator 122 is driven toa continuously on state, the PWM signal still continues to switchbetween on and off states.

The first feedback circuit 108 includes an error amplifier 126, areference voltage source 128, and a compensation network such as aresistor-capacitor circuit (RC) 130. The error amplifier 126 monitorsthe difference between the feedback (FB) signal and the voltagereference (Vref) signal to provide the compensation (COMP) signal. TheRC circuit 130 provides low-pass filtering so that the error amplifier126 remains stable over a wide range of frequency perturbations causedby output load and input voltage fluctuations.

The threshold voltage (Vth) is provided by a threshold generator 132that generates a threshold voltage Vth proportional to the outputvoltage (Vout). The ramp generator 114 creates a RAMP signal having aslew rate proportional to the input voltage (Vin). The output of theramp generator 114 is only coupled to an inverting input of the PWMcomparator during the on time of PWM pulses using the PWM signal thatgates the RAMP signal using transistors 134 and an inverter 136. Theramp generator 114 includes a trans-conductance device (Gon) thatgenerates a current proportional to the input voltage (Vin) that isapplied across a capacitor (Cramp). Therefore, the amplitude of the RAMPsignal is proportional to the Vin level and the on time of the PWMsignal to obtain adaptive pulse width control of PWM signal.

The feedback signal adaptive circuit 112 modifies the FB signalaccording to changes in the input voltage and a control signal which inthis particular embodiment, is coupled to the output of the switchingvoltage regulator 100. The feedback signal adaptive circuit 112 injectsan alternating current (AC) ripple voltage into the FB signal to adaptthe feedback loop of the second feedback circuit 110 according tochanges in input voltage (Vin) and the control signal. The feedbacksignal adaptive circuit 112 generally includes a trans-conductancedevice (Gin), which is gated by the PWM signal to charge a capacitor(Cripple) when the PWM signal is in a logic hi state. The feedbacksignal adaptive circuit 112 also includes a trans-conductance device(Gout) to discharge a capacitor (Cripple) according to the controlsignal. The capacitor (Cripple) and a resistor (Rripple) form a RCcircuit such that cyclic variations in voltage charged across thecapacitor (Cripple) are applied to an input of a trans-conductancedevice (Gfb). Trans-conductance device (Gfb) generates the AC ripplecurrent in response to the cyclic voltage variations formed across theresistor (Rripple). Thus, the FB signal may be adaptively modified tocompensate for transient changes in the input voltage (Vin) and voltagespresent on the control signal.

A capacitor (Cc) and a resistor (Rc) form a RC circuit for injecting theAC ripple voltage into the FB signal. That is, the capacitor (Cc) blocksdirect current (DC) bias in the feedback signal adaptive circuit 112from the FB signal in which the DC bias is generated across the resistor(Rc) and an offset voltage (Vos). The stability and dynamic response ofthe switching voltage regulator 100 may be adjusted by a feedbackresistor (RFB1). In continuous-conduction-mode (CCM), trans-conductancedevice (Gin) charges capacitor (Cripple) during PWM on time and thetrans-conductance device (Gout) discharges the capacitor (Cripple).Resistor (Rripple) provides a DC bias operation voltage from Vos toCripple. The trans-conductance device (Gfb) converts the voltagedifference (e.g., VCripple−Vos) into a current coupled into FB nodethrough capacitor (Cc). The resistor (Rc) provides a DC bias operationvoltage from the offset voltage (Vos) to the capacitor (Cc). In oneembodiment, time constants (τ) of the RC circuit formed by resistor(Rripple) and capacitor (Cripple) (e.g., Rripple*Cripple) and resistor(Rc) and capacitor (Cc) (e.g., Rc*Cc) are larger or significantly largerthan the CCM switching period. In another embodiment, the time constants(τ) of (Rripple*Cripple) and (Rc*Cc) are set to be relatively equal toone another.

Embodiments of the present disclosure may provide certain advantages notheretofore recognized by conventional switching voltage regulatortopologies. For example, use of the feedback signal adaptive circuit 112may alleviate the necessity of additional components that wouldotherwise be required for compensating a switching voltage regulator'sfeedback loop for stability under varying input and output conditions.Whereas traditional switching voltage regulator topologies have oftenrequired relatively large quantities of components to providecompensation, the feedback signal adaptive circuit 112 alleviates thisnecessity. In many cases, it is beneficial to implement switchingvoltage regulators in which some or most of their constituent componentscan be integrated into a single integrated circuit (IC) chip, thusincurring minimal external parts requirements. However, conventionalswitching voltage regulator topologies often require compensationcircuitry that needs to be implemented as discrete components, thusrequiring a relatively high parts count. The feedback signal adaptivecircuit 112 is easily integrated on the same monolithic substrate thatthe other components (e.g., first feedback circuit 108, second feedbackcircuit 110, gate drive circuit 102, ramp generator 114, etc.) areintegrated such that overall parts count may be minimized whileproviding effective compensation for the switching voltage regulator'sstable operation.

FIG. 2 illustrates another example switching voltage regulator 200 thatmay be provided with adaptive feedback control according to oneembodiment of the present disclosure. In general, the switching voltageregulator 200 includes a gate drive circuit 202, a switching circuit204, an inductor 206, a first feedback circuit 208, a second feedbackcircuit 210, a feedback signal adaptive circuit 212, and a rampgeneration circuit 214 that are similar in design and construction tothe gate drive circuit 102, switch circuit 104, inductor 106, firstfeedback circuit 108, second feedback circuit 110, feedback signaladaptive circuit 112, and ramp generation circuit 114, respectively, asshown and described above with respect to FIG. 1. The switching voltageregulator 200 differs, however, in that the control line is not coupledto the output voltage (Vout); rather, it is available for connection tosome other nodes like Vref which may be an output of a digital to analogconverter (DAC). Additionally, the Rfb2 resistor as shown in FIG. 1 doesnot need to be connected from the FB signal to ground. The switchingvoltage regulator 200 may be particularly suitable for DAC trackingapplications that may use a switching voltage regulator whose output canbe varied according to a control signal Vref.

FIG. 3 illustrates another example switching voltage regulator 300 thatmay be provided with adaptive feedback control according to oneembodiment of the present disclosure. the switching voltage regulator300 includes a gate drive circuit 302, a switching circuit 304, aninductor 306, a first feedback circuit 308, a second feedback circuit310, a feedback signal adaptive circuit 312, and a ramp generationcircuit 314 that are similar in design and construction to the gatedrive circuit 102, switching circuit 104, inductor 106, first feedbackcircuit 108, second feedback circuit 110, feedback signal adaptivecircuit 112, and ramp generation circuit 114, respectively, as shown anddescribed above with respect to FIG. 1. The switching voltage regulator300 differs, however, in that the control line is coupled to an outputof the switch circuit 304 rather than the output voltage (Vout). Thisparticular topology may be beneficial for applications that may notprovide easy access to direct sensing of the output voltage (Vout). Inthe present case, an estimated level of the output voltage (Vout) can beachieved by filtering the switching (SW) signal using a RC circuitformed by a capacitor 320 and a resistor 322.

Although the switching voltage regulators 100, 200, and 300 illustrateexample embodiments of circuits that may be used to provide adaptivefeedback control for voltage regulators, other embodiments may haveother topologies without departing from the spirit and scope of thepresent disclosure. For example, other embodiments may includeadditional components, fewer components, or different components thatwhat is described herein. Additionally, certain components of each ofthe example switching voltage regulators 100, 200, and 300 may beintegrated into a monolithic circuit chip, while other components areimplemented using discrete circuitry.

It is believed that the present disclosure and many of its attendantadvantages will be understood by the foregoing description, and it willbe apparent that various changes may be made in the form, construction,and arrangement of the components without departing from the disclosedsubject matter or without sacrificing all of its material advantages.The form described is merely explanatory, and it is the intention of thefollowing claims to encompass and include such changes.

While the present disclosure has been described with reference tovarious embodiments, it will be understood that these embodiments areillustrative and that the scope of the disclosure is not limited tothem. Many variations, modifications, additions, and improvements arepossible. More generally, embodiments in accordance with the presentdisclosure have been described in the context of particularimplementations. Functionality may be separated or combined in blocksdifferently in various embodiments of the disclosure or described withdifferent terminology. These and other variations, modifications,additions, and improvements may fall within the scope of the disclosureas defined in the claims that follow.

What is claimed is:
 1. An electrical circuit comprising: a first voltagefeedback circuit comprising an amplifier, the amplifier configured toreceive a feedback signal and a reference voltage and to generate acompensation signal according to the feedback signal and the referencevoltage; a second voltage feedback circuit comprising a comparator thatis configured to generate a Pulse Width Modulated (PWM) signal to drivea switch circuit, the comparator initiating the PWM pulse when thefeedback voltage goes lower than the compensation signal and ending thePWM pulse when the sum of the feedback signal and a ramp signal exceedsthe sum of the compensation signal and a threshold signal; and afeedback signal adaptive circuit having a first input for receiving thePWM signal, a second input for receiving the control signal, and a thirdinput for receiving an input voltage, the feedback signal adaptivecircuit configured to generate a ripple voltage according to the PWMsignal, a value of the input voltage, and a value of the control signal,generate a ripple current according to the ripple voltage, and modifythe feedback signal by coupling the ripple current to the feedbacksignal.
 2. The electrical circuit of claim 1, wherein the feedbacksignal adaptive circuit comprises a first trans-conductive device, asecond trans-conductive device, and a first resistor-capacitor (RC)circuit having a first capacitor and a first resistor, and wherein thefeedback signal adaptive circuit is configured to: charge the firstcapacitor using the first trans-conductance device and at a rateaccording to a voltage value of the input voltage during an on time ofthe PWM signal; discharge the first capacitor at a rate using the secondtrans-conductance device and according to a value of the control signalduring an off time of the PWM signal; and generate the ripple voltageacross the first resistor according to a voltage across the firstcapacitor.
 3. The electrical circuit of claim 2, wherein a first timeconstant associated with the first RC circuit is larger than a timeperiod of the PWM signal.
 4. The electrical circuit of claim 2, whereinthe feedback signal adaptive circuit further comprises a secondresistor-capacitor (RC) circuit having a second capacitor and a secondresistor, the second capacitor configured to inject the ripple currentinto the feedback signal and to block direct current (DC) bias in thefeedback signal adaptive circuit, the DC bias generated across thesecond resistor and an offset voltage.
 5. The electrical circuit ofclaim 4, wherein a second time constant associated with the second RCcircuit is larger than a time period of the PWM signal.
 6. Theelectrical circuit of claim 1, wherein the control signal is coupled toan output of a voltage regulator.
 7. The electrical circuit of claim 1,wherein the control signal is coupled to the output of the switchcircuit.
 8. The electrical circuit of claim 1, wherein the controlsignal is coupled to a reference voltage source, an output of a voltageregulator tracking the voltage of the reference.
 9. The electricalcircuit of claim 1, further comprising: a threshold generator thatgenerates the threshold signal proportional to the control signal; and aramp generator that generates the ramp signal having a slew rateproportional to the input voltage.
 10. A voltage regulating methodcomprising: receiving a feedback signal generated from an output of avoltage regulator; generating a compensation signal according to thefeedback signal and a reference voltage; generating a Pulse WidthModulation (PWM) signal to drive a switch circuit using a comparatorthat initiates the PWM pulse when the feedback voltage goes lower thanthe compensation signal and ends the PWM pulse when the sum of thefeedback signal and a ramp signal exceeds the sum of the compensationsignal and a threshold signal; generating a ripple current according tothe PWM signal, changes in an input voltage of the voltage regulator,and a control signal, wherein the output of the voltage regulator isgenerated from the input voltage; and modifying the feedback signal byinjecting, through a coupling capacitor, the ripple current into thefeedback signal.
 11. The voltage regulating method of claim 10, whereingenerating the ripple current comprises: charging a first capacitor of afirst resistor-capacitor (RC) circuit according to a voltage value ofthe input voltage during an on time of the PWM signal; discharging thefirst capacitor according to a voltage value of the control signalduring an off time of the PWM signal; generating, using a voltage acrossthe first capacitor, a ripple voltage across a first resistor of thefirst RC circuit; and generating the ripple current according to theripple voltage.
 12. The voltage regulating method of claim 11, wherein afirst time constant associated with the first RC circuit is larger thana time period of the PWM signal.
 13. The voltage regulating method ofclaim 10, wherein the control signal is coupled to the output of thevoltage regulator.
 14. The voltage regulating method of claim 10,wherein the control signal is coupled to the output of the switchcircuit.
 15. The voltage regulating method of claim 10, wherein thecontrol signal is coupled to a reference voltage source, the output ofthe voltage regulator tracking the voltage of the reference.
 16. Thevoltage regulating method of claim 10, further comprising: generatingthe threshold signal proportional to the control signal; and generatingthe ramp signal having a slew rate proportional to the input voltage.17. An electrical circuit comprising: a threshold generator circuit thatis configured to generate a threshold signal according to a controlsignal; a ramp generator circuit that is configured to generate a rampsignal with a slew rate to be proportional to an input voltage of avoltage regulator; a first voltage feedback circuit comprising anamplifier, the amplifier configured to receive a feedback signal and areference voltage and to generate a compensation signal according to thefeedback signal and the reference voltage; and a second voltage feedbackcircuit comprising a comparator that is configured to generate a PulseWidth Modulation (PWM) signal to drive a switch circuit, the comparatorinitiating the PWM pulse when the feedback voltage goes lower than thecompensation signal and ending the PWM pulse when the sum of thefeedback signal and the ramp signal exceeds the sum of the compensationsignal and the threshold signal; and a feedback signal adaptive circuitcomprising: a first resistor-capacitor (RC) circuit having a firstcapacitor and a first resistor coupled to the first capacitor, the firstcapacitor configured to be charged according to a voltage value of theinput voltage during an on time of the PWM signal and dischargedaccording to a voltage value of the control signal during an off time ofthe PWM signal, wherein the feedback signal adaptive circuit modifiesthe feedback signal according to changes in voltage across the firstresistor, wherein a first time constant associated with the first RCcircuit is substantially larger than a time period of the PWM signal;and a second capacitor configured to capacitively couple the feedbacksignal adaptive circuit to the feedback signal, wherein the electricalcircuit generates an output of the voltage regulator from the inputvoltage.